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For some types of BPF programs that utilize expected_attach_type, libbpf won't set load_attr.expected_attach_type, even if expected_attach_type is known from section definition. This was done to preserve backwards compatibility with old kernels that didn't recognize expected_attach_type attribute yet (which was added in5e43f899b0("bpf: Check attach type at prog load time"). But this is problematic for some BPF programs that utilize newer features that require kernel to know specific expected_attach_type (e.g., extended set of return codes for cgroup_skb/egress programs). This patch makes libbpf specify expected_attach_type by default, but also detect support for this field in kernel and not set it during program load. This allows to have a good metadata for bpf_program (e.g., bpf_program__get_extected_attach_type()), but still work with old kernels (for cases where it can work at all). Additionally, due to expected_attach_type being always set for recognized program types, bpf_program__attach_cgroup doesn't have to do extra checks to determine correct attach type, so remove that additional logic. Also adjust section_names selftest to account for this change. More detailed discussion can be found in [0]. [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/ Fixes:5cf1e91456("bpf: cgroup inet skb programs can return 0 to 3") Fixes:5e43f899b0("bpf: Check attach type at prog load time") Reported-by: Andrey Ignatov <rdna@fb.com> Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Song Liu <songliubraving@fb.com> Acked-by: Andrey Ignatov <rdna@fb.com> Link: https://lore.kernel.org/bpf/20200414182645.1368174-1-andriin@fb.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.